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Publication numberUS7332211 B1
Publication typeGrant
Application numberUS 10/400,907
Publication dateFeb 19, 2008
Filing dateMar 28, 2003
Priority dateNov 7, 2002
Fee statusPaid
Also published asUS8535758, US20130216707
Publication number10400907, 400907, US 7332211 B1, US 7332211B1, US-B1-7332211, US7332211 B1, US7332211B1
InventorsVladimir Bulovic, Seth A. Coe, Wing-Keung Woo, Moungi G. Bawendi
Original AssigneeMassachusetts Institute Of Technology
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Layered materials including nanoparticles
US 7332211 B1
Abstract
A composition includes a layer of nanoparticles and a layer of a second material.
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Claims(15)
1. A composition comprising:
a matrix material and a plurality of nanoparticles phase separated from the matrix material, wherein the matrix material and the nanoparticles are chemically dissimilar, and wherein the matrix material and the nanoparticles are soluble in a mutual solvent.
2. The composition of claim 1, wherein the matrix material forms a layer.
3. The composition of claim 2, wherein the layer of matrix material is discontinuous.
4. The composition of claim 1, wherein the plurality of nanoparticles form a layer contacting the matrix material.
5. The composition of claim 4, wherein the layer of nanoparticles is discontinuous.
6. The composition of claim 1, wherein the plurality of nanoparticles is a plurality of semiconductor nanoparticles.
7. The composition of claim 1, wherein the plurality of nanoparticles is a plurality of metallic nanoparticles.
8. The composition of claim 1, wherein the plurality of nanoparticles is a plurality of ceramic nanoparticles.
9. The composition of claim 1, wherein the layer of nanoparticles is a monolayer.
10. The composition of claim 1, wherein the matrix material is non-polymeric.
11. The composition of claim 1, wherein each nanoparticle has a ligand bonded to a surface of the nanoparticle having the formula:
wherein k is 2, 3 or 5, and n is 1, 2, 3, 4 or 5 such that k-n is not less than zero; X is O, S, S═O, SO2, Se, Se=O, N,N=O, P, P=O, As, or As=O; each of Y and L, independently, is aryl, heteroaryl, or a straight or branched C2-12 hydrocarbon chain optionally containing at least one double bond, at least one triple bond, or at least one double bond and one triple bond, the hydrocarbon chain being optionally substituted with one or more C1-4 alkyl, C2-4 alkenyl, C2-4 alkynyl, C1-4 alkoxy, hydroxyl, halo, amino, nitro, cyano, C3-5 cycloalkyl, 3-5 membered heterocycloalkyl, aryl, heteroaryl, C1-4 alkylcarbonyloxy, C1-4 alkyloxycarbonyl, C1-4 alkylcarbonyl, or formyl and the hydrocarbon chain being optionally interrupted by O, S, N(Ra), N(Ra)C(O)O, OC(O)N(Ra), N(Ra)C(O)N(Rb), OC(O)O, P(Ra), or P(O)(Ra); and each of Ra and Rb, independently, is hydrogen, alkyl, alkenyl, alkynyl, alkoxy, hydroxylalkyl, hydroxyl, or haloalkyl.
12. The composition of claim 1, wherein the matrix material includes an aromatic moiety.
13. The composition of claim 12, wherein each nanoparticle has a ligand bonded to a surface of the nanoparticle, the ligand including an aliphatic moiety.
14. A composition comprising:
a matrix material and a plurality of nanoparticles phase separated from the matrix material, wherein the composition includes a structure comprising at least a portion of the nanoparticles on the matrix material.
15. The composition of claim 14, wherein the structure includes a nanocrystal island on the matrix material.
Description
CLAIM OF PRIORITY

This application claims priority under 35 USC 119(e) to U.S. Patent Application Ser. No. 60/424,343, filed on Nov. 7, 2002, the entire contents of which are hereby incorporated by reference.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under Grant No. DMR-9808941, awarded by the NSF. The government has certain rights in the invention.

TECHNICAL FIELD

The present invention relates to materials including nanoparticles.

BACKGROUND

In general, a composite is a material that contains two or more components. Each component can contribute unique properties to the composite. As a result, the composite can have the advantageous properties of each component, all of which would not be present in a material that is lacking one of the components. Some composite materials can be particularly well-suited for use, for example, in optical, electronic, optoelectronic, magnetic, or catalytic applications.

SUMMARY

A composition can include a matrix material and a plurality of nanoparticles phase separated from the matrix material. The matrix material can form a layer. The layer can be discontinuous. The plurality of nanoparticles can form a layer contacting the matrix material. The layer of nanoparticles can be discontinuous.

A method of manufacturing a layered device can include depositing a film-forming solution on a substrate to form two layers from the film-forming solution, the film-forming solution including a first material and a second material. The first material includes a matrix material and the second material includes a plurality of nanoparticles. One layer can be a discontinuous or continuous layer including the nanoparticles.

The matrix can be non-polymeric. The nanoparticle can be a nanocrystal. The nanoparticles can be metallic nanoparticles, ceramic nanoparticles, or semiconductor nanoparticles, such as semiconductor nanocrystals. The plurality of nanoparticles can be a substantially monodisperse population of semiconductor nanoparticles.

In another aspect, a method of forming a layered structure includes selecting a matrix material and a nanoparticle which are mutually immiscible, dissolving the matrix material and the nanoparticle in a solvent to form a coating solution, and coating a substrate with the coating solution. Coating the substrate with the coating solution can include spin coating. The nanoparticle can be a semiconductor nanoparticle, a metallic nanoparticle, or a ceramic nanoparticle. The nanoparticle can be one of a plurality of nanoparticles forming a monolayer on a layer of the matrix material.

Typical conventional thin film deposition of solvated materials involves spin-casting of individual materials to form a multilayered (e.g., bilayered) structure. The disadvantages inherent to the spin-casting process to form a multilayered structure are due to the presence of the solvent. For example, in order to deposit a multilayered structure using spin-casting, care must be taken to choose a solvent of the overlayer to avoid dissolving the underlying film. By using phase segregation, bilayered or other multilayered structures can be manufactured in a single film deposition step.

The material can include greater than 0.001%, greater than 0.01%, greater than 0.1%, greater than 1%, greater than 5%, greater than 10%, greater than 50%, or greater than 90% by volume nanoparticles. The material can form a layer of a light emitting device. Light emitting devices including semiconductor nanocrystals are described, for example, in U.S. Application No. 60/368,130, filed Mar. 29, 2002, which is incorporated by reference in its entirety.

Metallic nanoparticles can be prepared as described, for example, in U.S. Pat. No. 6,054,495, which is incorporated by reference in its entirety. The metallic nanoparticle can be a noble metal nanoparticle, such as a gold nanoparticle. Gold nanoparticles can be prepared as described in U.S. Pat. No. 6,506,564, which is incorporated by reference in its entirety. Ceramic nanoparticles can be prepared as described, for example, in U.S. Pat. No. 6,139,585, which is incorporated by reference in its entirety.

Narrow size distribution, high quality semiconductor nanocrystals with high fluorescence efficiency are first prepared using previously established literature procedures and used as the building blocks. See, C. B. Murray et al., J. Amer. Chem. Soc. 1993, 115, 8706, B. O. Dabbousi et al., J. Phys. Chem. B 1997, 101, 9463, each of which is incorporated by reference in its entirety. The organic, surface-passivating ligands are then exchanged to stabilize the nanocrystals in polar solvents and in the matrix. The each of the plurality of semiconductor nanocrystals includes a same or different first semiconductor material. Each first semiconductor material can be overcoated with a second semiconductor material. Each first semiconductor film has a first band gap and each second semiconductor material has a second band gap. The second band gap can be larger than the first band gap. Each nanocrystal can have a diameter of less than about 10 nanometers. The plurality of nanocrystals can have a monodisperse distribution of sizes.

Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic drawing depicting a light-emitting device.

FIGS. 2A-2F are atomic force microscopy (AFM) images showing the surface morphology of various organic/nanoparticle films. a) Phase image of a partial monolayer of nanocrystals on N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD) after phase segregation during spin-coating. Nanoparticle surface coverage is 21%. b) Height image of a close-up of (a) showing both an island of nanoparticles as well as individual nanoparticles on a flat TPD background. c) Phase image of a complete, hexagonally packed monolayer of nanoparticles phase segregated from the underlying TPD. Grain boundaries between ordered domains of nanoparticles are observable. d) Phase image of TPD and nanoparticles after thermal evaporation of nominal 5 nm of TPD onto the complete nanoparticle layer of (c). Material phase segregation results in TPD droplet formation. e) Phase image of nominal 10 nm of 3-(4-biphenylyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole (TAZ) on surface similar to (c). TAZ surface coverage is 72%. f) Height image of nominal 40 nm of Alq3 on surface similar to (c). Coverage is complete, with an rms surface roughness of 0.56 mm.

DETAILED DESCRIPTION

Chemically synthesized colloidal nanoparticles (nanoparticles), such as semiconductor nanocrystals or quantum dots, consist of 1-10 nm diameter particles decorated with a layer of organic ligands. See, C. B. Murray et al., Annu. Rev. Mat. Sci., 30, 545-610 (2000), which is incorporated in its entirety. These zero-dimensional structures show strong quantum confinement effects that can be harnessed in designing bottom-up chemical approaches to create complex heterostructures with electronic and optical properties that are tunable with the size of the nanocrystals. At the same time, as a result of the surrounding ligand shell, nanocrystals can be chemically manipulated as large molecules.

The chemical properties of the surrounding ligand shell can make the nanoparticles soluble within or reactive with a matrix material. The matrix material can be an inorganic material or an organic material. The surrounding ligand shell has exposed ligand moieties. When the exposed ligand moieties are chemically similar to the matrix material, the nanoparticles are soluble in the matrix. When the exposed ligand moieties and matrix material are chemically dissimilar, the nanoparticles are not soluble within the matrix. The ligand moieties can have the formula:


wherein k is 2, 3 or 5, and n is 1, 2, 3, 4 or 5 such that k-n is not less than zero; X is O, S, S=O, SO2, Se, Se=O, N,N=O, P, P=O, As, or As=O; each of Y and L, independently, is aryl, heteroaryl, or a straight or branched C2-12 hydrocarbon chain optionally containing at least one double bond, at least one triple bond, or at least one double bond and one triple bond, the hydrocarbon chain being optionally substituted with one or more C1-4 alkyl, C2-4 alkenyl, C2-4 alkynyl, C1-4 alkoxy, hydroxyl, halo, amino, nitro, cyano, C3-5 cycloalkyl, 3-5 membered heterocycloalkyl, aryl, heteroaryl, C1-4 alkylcarbonyloxy, C1-4 alkyloxycarbonyl, C1-4 alkylcarbonyl, or formyl and the hydrocarbon chain being optionally interrupted by O, S, N(Ra), N(Ra)C(O)O, OC(O)N(Ra), N(Ra)C(O)N(Rb), OC(O)O, P(Ra), or P(O)(Ra); and each of Ra and Rb, independently, is hydrogen, alkyl, alkenyl, alkynyl, alkoxy, hydroxylalkyl, hydroxyl, or haloalkyl.

An aryl group is a substituted or unsubstituted cyclic aromatic group. Examples include phenyl, benzyl, naphthyl, tolyl, anthracyl, nitrophenyl, or halophenyl. A heteroaryl group is an aryl group with one or more heteroatoms in the ring, for instance furyl, pyiridyl, pyrrolyl, or phenanthryl.

A suitable coordinating ligand can be purchased commercially or prepared by ordinary synthetic organic techniques, for example, as described in J. March, Advanced Organic Chemistry, which is incorporated by reference in its entirety.

When the exposed ligand moieties and the matrix material are chemically dissimilar, a phase segregated material can be produced. The nanoparticles having the ligand shell with exposed ligand moieties and a chemically dissimilar matrix material can be dissolved in a mutual solvent to generate a film-forming solution. The solution can be deposited on a substrate, for example, by drop coating, dip coating or spin coating, to form a film. When dried, the film contains a layer of matrix material and a layer of nanoparticles. Either layer may be discontinuous, depending on the concentration of the nanoparticles or matrix material in the film-forming solution. For example, if the nanoparticles form a discontinuous layer, the nanoparticles form islands of a higher concentration of nanoparticles contacting a continuous layer of matrix material. In this manner, multiple layers are formed in a single film-forming deposition step.

Material phase segregation can be used to create a spin-cast thin film bilayer structure. The chemical characteristics of the two components are chosen so that layered phase segregation results. For example, a bilayer structure consisting of a bottom layer of N, N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD) is covered with a layer of self-assembled colloidal semiconductor nanocrystals as a monolayer. The TPD consists in large part of aromatic groups, while the nanoparticles have a ligand shell that exposes a surface which mostly consists of alkyl chains (trioctylphosphine/trioctylphosphine oxide). There can also be a large size difference between the molecular matrix, typically about 1 nm or less, and the colloidal nanoparticles, typically greater than 3 nm. While this example employs aromatic/aliphatic chemical pairs, any pair of moieties or functional groups can be used such that phase separation will occur. For example, nanoparticles that would display a highly polar surface (e.g. OH groups) can phase separate in a layered film upon spin-coating if the other molecule is mostly non-polar. The bilayer structure can used to fabricate efficient light emitting devices (LEDs).

The solubility of the nanoparticles and matrix material in the solvent can be on the order of 10 mg/mL to allow for a large range of possible solution mixtures and film thicknesses. Additionally, the matrix material can be selected to maximize phase segregation with the nanoparticles.

When the material is included in a light emitting device, the device can include two layers separating two electrodes of the device. The material of one layer can be chosen based on the material's ability to transport holes, or the hole transporting layer (HTL). The material of the other layer can be chosen based on the material's ability to transport electrons, or the electron transporting layer (ETL). The electron transporting layer typically includes an electroluminescent layer. When a voltage is applied, one electrode injects holes (positive charge carriers) into the hole transporting layer, while the other electrode injects electrons into the electron transporting layer. The injected holes and electrons each migrate toward the oppositely charged electrode. When an electron and hole localize on the same molecule, an exciton is formed, which can recombine to emit light.

A light emitting device can have a structure such as shown in FIG. 1, in which a first electrode 2, a first layer 3 in contact with the electrode 2, a second layer 4 in contact with the first layer 3, and a second electrode 5 in contact with the second layer 4. First layer 3 can be a hole transporting layer and second layer 4 can be an electron transporting layer. Alternatively, a separate emissive layer (not shown in FIG. 1) can be included between the hole transporting layer and the electron transporting layer. One of the electrodes of the structure is in contact with a substrate 1. Each electrode can contact a power supply to provide a voltage across the structure. Electroluminescence can be produced by the emissive layer of the heterostructure when a voltage of proper polarity is applied across the heterostructure. First layer 3 can include a plurality of nanoparticles, for example, a substantially monodisperse population of nanoparticles. Alternatively, a separate emissive layer can include the plurality of nanoparticles.

Emission from semiconductor nanocrystals can occur at an emission wavelength when one or more of the nanocrystals is excited. The emission has a frequency that corresponds to the band gap of the quantum confined semiconductor material. The band gap is a function of the size of the nanocrystal. Nanocrystals having small diameters can have properties intermediate between molecular and bulk forms of matter. For example, nanocrystals based on semiconductor materials having small diameters can exhibit quantum confinement of both the electron and hole in all three dimensions, which leads to an increase in the effective band gap of the material with decreasing crystallite size. Consequently, both the optical absorption and emission of nanocrystals shift to the blue (i.e., to higher energies) as the size of the crystallites decreases.

The emission from the nanocrystal can be a narrow Gaussian emission band that can be tuned through the complete wavelength range of the ultraviolet, visible, or infrared regions of the spectrum by varying the size of the nanocrystal, the composition of the nanocrystal, or both. For example, CdSe can be tuned in the visible region and InAs can be tuned in the infrared region. The narrow size distribution of a population of nanocrystals can result in emission of light in a narrow spectral range. The population can be monodisperse and can exhibit less than a 15% rms deviation in diameter of the nanocrystals, preferably less than 10%, more preferably less than 5%. Spectral emissions in a narrow range of no greater than about 75 nm, preferably 60 nm, more preferably 40 nm, and most preferably 30 nm full width at half max (FWHM) can be observed. The breadth of the emission decreases as the dispersity of nanocrystal diameters decreases.

Semiconductor nanocrystals can have high emission quantum efficiencies such as greater than 10%, 20%, 30%, 40%, 50%, 60%, 70%, or 80%. The semiconductor forming the nanocrystals can include Group II-VI compounds, Group II-V compounds, Group III-VI compounds, Group III-V compounds, Group IV-VI compounds, Group I-III-VI compounds, Group II-IV-VI compounds, or Group II-IV-V compounds, for example, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, GaSe, InN, InP, InAs, InSb, TlN, TlP, TlAs, TlSb, PbS, PbSe, PbTe, or mixtures thereof.

Methods of preparing monodisperse semiconductor nanocrystals include pyrolysis of organometallic reagents, such as dimethyl cadmium, injected into a hot, coordinating solvent. This permits discrete nucleation and results in the controlled growth of macroscopic quantities of nanocrystals. Preparation and manipulation of nanocrystals are described, for example, in U.S. Pat. No. 6,322,901, which is incorporated herein by reference in its entirety. The method of manufacturing a nanocrystal is a colloidal growth process. Colloidal growth occurs by rapidly injecting an M donor and an X donor into a hot coordinating solvent. The injection produces a nucleus that can be grown in a controlled manner to form a nanocrystal. The reaction mixture can be gently heated to grow and anneal the nanocrystal. Both the average size and the size distribution of the nanocrystals in a sample are dependent on the growth temperature. The growth temperature necessary to maintain steady growth increases with increasing average crystal size. The nanocrystal is a member of a population of nanocrystals. As a result of the discrete nucleation and controlled growth, the population of nanocrystals obtained has a narrow, monodisperse distribution of diameters. The monodisperse distribution of diameters can also be referred to as a size. The process of controlled growth and annealing of the nanocrystals in the coordinating solvent that follows nucleation can also result in uniform surface derivatization and regular core structures. As the size distribution sharpens, the temperature can be raised to maintain steady growth. By adding more M donor or X donor, the growth period can be shortened.

The M donor can be an inorganic compound, an organometallic compound, or elemental metal. M is cadmium, zinc, magnesium, mercury, aluminum, gallium, indium or thallium. The X donor is a compound capable of reacting with the M donor to form a material with the general formula MX. Typically, the X donor is a chalcogenide donor or a pnictide donor, such as a phosphine chalcogenide, a bis(silyl) chalcogenide, dioxygen, an ammonium salt, or a tris(silyl) pnictide. Suitable X donors include dioxygen, bis(trimethylsilyl) selenide ((TMS)2Se), trialkyl phosphine selenides such as (tri-n-octylphosphine) selenide (TOPSe) or (tri-n-butylphosphine) selenide (TBPSe), trialkyl phosphine tellurides such as (tri-n-octylphosphine) telluride (TOPTe) or hexapropylphosphorustriamide telluride (HPPTTe), bis(trimethylsilyl)telluride ((TMS)2Te), bis(trimethylsilyl)sulfide ((TMS)2S), a trialkyl phosphine sulfide such as (tri-n-octylphosphine) sulfide (TOPS), an ammonium salt such as an ammonium halide (e.g., NH4Cl), tris(trimethylsilyl) phosphide ((TMS)3P), tris(trimethylsilyl) arsenide ((TMS)3As), or tris(trimethylsilyl)antimonide ((TMS)3Sb). In certain embodiments, the M donor and the X donor can be moieties within the same molecule.

A coordinating solvent can help control the growth of the nanocrystal. The coordinating solvent is a compound having a donor lone pair that, for example, has a lone electron pair available to coordinate to a surface of the growing nanocrystal. Solvent coordination can stabilize the growing nanocrystal. Typical coordinating solvents include alkyl phosphines, alkyl phosphine oxides, alkyl phosphonic acids, or alkyl phosphinic acids, however, other coordinating solvents, such as pyridines, furans, and amines may also be suitable for the nanocrystal production. Examples of suitable coordinating solvents include pyridine, tri-n-octyl phosphine (TOP), tri-n-octyl phosphine oxide (TOPO) and tris-hydroxylpropylphosphine (tHPP). Technical grade TOPO can be used.

Size distribution during the growth stage of the reaction can be estimated by monitoring the absorption line widths of the particles. Modification of the reaction temperature in response to changes in the absorption spectrum of the particles allows the maintenance of a sharp particle size distribution during growth. Reactants can be added to the nucleation solution during crystal growth to grow larger crystals. By stopping growth at a particular nanocrystal average diameter and choosing the proper composition of the semiconducting material, the emission spectra of the nanocrystals can be tuned continuously over the wavelength range of 300 nm to 5 microns, or from 400 nm to 800 nm for CdSe and CdTe. The nanocrystal has a diameter of less than 150 Å. A population of nanocrystals has average diameters in the range of 15 Å to 125 Å.

The nanocrystal can be a member of a population of nanocrystals having a narrow size distribution. The nanocrystal can be a sphere, rod, disk, or other shape. The nanocrystal can include a core of a semiconductor material. The nanocrystal can include a core having the formula MX, where M is cadmium, zinc, magnesium, mercury, aluminum, gallium, indium, thallium, or mixtures thereof, and X is oxygen, sulfur, selenium, tellurium, nitrogen, phosphorus, arsenic, antimony, or mixtures thereof.

The core can have an overcoating on a surface of the core. The overcoating can be a semiconductor material having a composition different from the composition of the core. The overcoat of a semiconductor material on a surface of the nanocrystal can include a Group II-VI compounds, Group II-V compounds, Group III-VI compounds, Group III-V compounds, Group IV-VI compounds, Group I-III-VI compounds, Group II-IV-VI compounds, and Group II-IV-V compounds, for example, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, GaSe, InN, InP, InAs, InSb, TlN, TlP, TlAs, TlSb, PbS, PbSe, PbTe, or mixtures thereof. For example, ZnS, ZnSe or CdS overcoatings can be grown on CdSe or CdTe nanocrystals. An overcoating process is described, for example, in U.S. Pat. No. 6,322,901. By adjusting the temperature of the reaction mixture during overcoating and monitoring the absorption spectrum of the core, over coated materials having high emission quantum efficiencies and narrow size distributions can be obtained.

The particle size distribution can be further refined by size selective precipitation with a poor solvent for the nanocrystals, such as methanol/butanol as described in U.S. Pat. No. 6,322,901. For example, nanocrystals can be dispersed in a solution of 10% butanol in hexane. Methanol can be added dropwise to this stirring solution until opalescence persists. Separation of supernatant and flocculate by centrifugation produces a precipitate enriched with the largest crystallites in the sample. This procedure can be repeated until no further sharpening of the optical absorption spectrum is noted. Size-selective precipitation can be carried out in a variety of solvent/nonsolvent pairs, including pyridine/hexane and chloroform/methanol. The size-selected nanocrystal population can have no more than a 15% rms deviation from mean diameter, preferably 10% rms deviation or less, and more preferably 5% rms deviation or less.

The outer surface of the nanocrystal can include a layer of compounds derived from the coordinating solvent used during the growth process. The surface can be modified by repeated exposure to an excess of a competing coordinating group to form an overlayer. For example, a dispersion of the capped nanocrystal can be treated with a coordinating organic compound, such as pyridine, to produce crystallites which disperse readily in pyridine, methanol, and aromatics but no longer disperse in aliphatic solvents. Such a surface exchange process can be carried out with any compound capable of coordinating to or bonding with the outer surface of the nanocrystal, including, for example, phosphines, thiols, amines and phosphates. The nanocrystal can be exposed to short chain polymers which exhibit an affinity for the surface and which terminate in a moiety having an affinity for a suspension or dispersion medium. Such affinity improves the stability of the suspension and discourages flocculation of the nanocrystal.

Layers including nanocrystals can be formed by redispersing the powder semiconductor nanocrystals described above in a solvent system and drop casting films of the nanocrystals from the dispersion. The solvent system for drop casting depends on the chemical character of the outer surface of the nanocrystal, i.e., whether or not the nanocrystal is readily dispersible in the solvent system. The drop cast films are dried in an inert atmosphere for about 12 to 24 hours before being dried under vacuum. Typically, the films are formed on substrates.

Transmission electron microscopy (TEM) can provide information about the size, shape, and distribution of the nanocrystal population. Powder x-ray diffraction (XRD) patterns can provided the most complete information regarding the type and quality of the crystal structure of the nanocrystals. Estimates of size are also possible since particle diameter is inversely related, via the X-ray coherence length, to the peak width. For example, the diameter of the nanocrystal can be measured directly by transmission electron microscopy or estimated from x-ray diffraction data using, for example, the Scherrer equation. It also can be estimated from the UV/Vis absorption spectrum.

Nanocrystals of CdSe coated with a ZnS passivation layer can have photoluminescence quantum efficiencies of as high as 50%, matching that of the best organic lumophores. See, for example, Hines et al., J. Phys. Chem. 100, 468 (1996), which is incorporated by reference in its entirety. By changing the diameter of the CdSe core from 23 to 55 Å, the luminescence wavelength can be precisely tuned from 470 nm to 640 nm with a typical spectral full width at half of maximum (FWHM) of less than 40 nm. See, for example, Dabbousi et al., J. Phys. Chem. 101, 9463 (1997), which is incorporated by reference in its entirety. The narrow FWHM of nanocrystals can result in saturated color emission. This can lead to efficient nanocrystal-light emitting devices even in the red and blue parts of the spectrum, since in nanocrystal emitting devices no photons are lost to infrared and UV emission. The broadly tunable, saturated color emission over the entire visible spectrum of a single material system is unmatched by any class of organic chromophores. Furthermore, environmental stability of covalently bonded inorganic nanocrystals suggests that device lifetimes of hybrid organic/inorganic light emitting devices should match or exceed that of all-organic light emitting devices, when nanocrystals are used as luminescent centers. The degeneracy of the band edge energy levels of nanocrystals facilitates capture and radiative recombination of all possible excitons, whether generated by direct charge injection or energy transfer. The maximum theoretical nanocrystal-light emitting device efficiencies are therefore comparable to the unity efficiency of phosphorescent organic light emitting devices. The nanocrystal's excited state lifetime (τ) is much shorter (τ≈10 ns) than a typical phosphor (τ>0.5 μs), enabling nanocrystal-light emitting devices to operate efficiently even at high current density.

The choice of organic host for the nanocrystals is limited by material deposition methods. CdSe nanocrystals are typically arranged into thin films by spin-casting from solution. While spin-casting is possible for molecular organics, and typical for polymer organics, it limits the available organic matrix materials to those that are highly soluble in solvents such as toluene, hexanes and chloroform, which are the preferred solvents for the TOPO capped nanocrystal colloids. In order to have a large range of possible solution mixtures and film thicknesses, it is necessary to have organic solubility in the range of 10 mg/mL. Such is the case for TPD in chloroform. TPD has the added advantage of being a blue emitting material, which can facilitate access to the entire visible spectrum by doping different sized nanocrystals into this organic matrix.

In one example of forming a bilayer, TPD and nanocrystals can be dispersed in a suitable solvent (chloroform in this case); the mixed solution is spin-cast on top of pre-cleaned ITO substrates. The phenyl/benzyl groups of the TPD and the alkyl groups covering the nanocrystal surfaces cause the two materials to phase segregate and result in the formation of a TPD/nanocrystal bilayer structure while the chloroform evaporates. The spin-casting is performed in a controlled (oxygen-free and moisture-free) environment in order to obtain highly reproducible heterostructures. Appropriate layer(s) of molecular organics followed by the metal electrode layers are then deposited via thermal evaporation. The self-assembled nanocrystal monolayer can be positioned in the recombination zone of the multilayer active organic electroluminescent device. Confinement of nanocrystals to the device active region maximizes the efficiency of nanocrystals material usage.

The process is very general. For example, controlled phase separation has been successful with CdSe, CdSe(ZnS), and PbSe nanocrystals with TOPO capping ligands, and oleic acid capping ligands. The matrix of the controlled phase separated structures can be organic molecules, such as N,N′-di-[(1-naphthalenyl)-N,N′-diphenyl]-1,1′-biphenyl)-4,4′-diamine (NPD) and TPD, as well as a polymerized version of TPD. Controlled phase separation has been successful using different solvents, including chloroform and chlorobenzene. Changing the size of the nanocrystals, for example, from 3 nm to 9 nm continued to result in efficient phase separation. In terms of controlling the process, lower vapor pressure solvents, which take longer to evaporate during spin coating, increase the degree of order found on the monolayer film of nanocrystals. For example, the nanocrystals can become hexagonally packed. Also, very narrow size distributions of nanocrystals increase the degree of observed hexagonal ordering in the nanocrystal layer.

Nanocrystal concentration can be adjusted to form a complete single monolayer on top of a TPD film that is 36 nm thick. Atomic force microscopy (AFM) images in FIGS. 2A and 2B show the result of spinning at ⅕ of the optimal concentration for a single monolayer, and confirm that TPD and nanocrystals do phase segregate during the spinning process, yielding a coverage of 21%. FIG. 2C shows a complete nanocrystal monolayer on a TPD film. Absorption measurements of these bilayers confirm that all of the nanocrystals are accounted for by this self-assembled, phase segregated monolayer. More particularly, FIGS. 2A-C are AFM images showing the surface morphology of various organic/nanocrystal films. a) Phase image of a partial monolayer of nanocrystals on TPD after phase segregation during spin-coating. Nanocrystal surface coverage is 21%. b) Height image of a close-up of (a) showing both an island of nanocrystals as well as individual nanocrystals on a flat TPD background. c) Phase image of a complete, hexagonally packed monolayer of nanocrystals phase segregated from the underlying TPD. Grain boundaries between ordered domains of nanocrystals are observable.

Optical absorption measurements of these bilayers indicate that nanocrystals make up 5-10% by volume of the 40 nm thick films, confirming that all of the nanocrystals are accounted for by this self-assembled, phase segregated monolayer. Further confirmation of the phase segregation process is shown in FIG. 2D, where after thermal evaporation of 5 nm of TPD onto the nanocrystal monolayer the TPD forms droplets rather than a planar thin film. Thicker organic overlayers can be planar, as in FIG. 2F, which shows the smooth surface of the 40 nm thick tris-(8-hydroxyquinoline)aluminum (Alq3) overlayer in a device similar to that shown in FIG. 1.

In such a device, holes are injected from the indium tin oxide (ITO) contact into the TPD host matrix and are transported towards the single nanocrystal monolayer. Similarly, electrons are injected from the Mg:Ag cathode into the Alq3 and are transported to the nanocrystals. Exciton generation on nanocrystals occurs via two parallel processes: direct charge injection and exciton energy transfer from organic molecules. For direct charge injection, electrons may be trapped at the nanocrystals due to the relative energy alignment of the lowest unoccupied molecular orbital (LUMO) levels of TPD, Alq3 and the nanocrystals. For these charged nanocrystals the barrier to hole injection from the TPD is reduced. Upon acceptance of holes from TPD, excitons form on the nanocrystals, and can subsequently recombine radiatively. Alternatively, excitons can be formed on organic molecules that are near grain boundaries, interstitial spaces, and voids in the single nanocrystal monolayer. These excitons can then energy transfer to the lower energy nanocrystal sites, where they recombine radiatively.

Although we observed the energy transfer process in the photoluminescence (PL) studies of TPD/nanocrystal films, the nanocrystal-LED current-voltage data suggests generation of excitons on QDs via direct charge injection. Comparing the current-voltage characteristics of the device with that of a control structure, without the monolayer of nanocrystals, shows that the nanocrystal-LED operates at a consistently higher voltage. The nanocrystal monolayer, therefore, inhibits charge conduction, which suggests charge trapping on nanocrystal sites. For devices with nanocrystal layer thicker than a single monolayer, the operating voltage increases further while the quantum efficiency is dramatically reduced. This is consistent with the low efficiency and the high operating voltage measured in earlier studies that examined nanocrystal-LEDs containing more than 10 layers of nanocrystals. Indeed, charge trapping at nanocrystal sites has been observed in recent luminescence quenching studies of charged nanocrystals. In addition, devices that have only a partial monolayer of nanocrystals have emission spectra that are dominated by Alq3 or TPD, indicating that precise control of the assembly of a nanocrystal monolayer can be important to device operation.

Sheets of single nanocrystal monolayers, square centimeters in size, can be employed in electrically active devices, minimizing nanocrystal material use to the active device region. The material phase segregation that governs formation of the organic/nanocrystal spin-cast thin film bilayers is a general and widely applicable fabrication process. The process is governed by the physical size and chemical character of the two solvated constituents; the TPD molecules are small (1 nm) and have aromatic character, while the nanocrystals are large in comparison (>3 nm) and present a surface that consists of mostly alkyl chains. In general, phase segregation is not limited to aromatic/aliphatic pairs, but governs the interaction between any pair of materials with disparate chemical functionality.

Other embodiments are within the scope of the following claims.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3156369Sep 19, 1962Nov 10, 1964Ethicon IncBicameral container
US4515267Nov 16, 1983May 7, 1985Dentsply Research & Development Corp.Dental mixing and extrusion capsule
US5027872 *Aug 11, 1989Jul 2, 1991Imperial Chemical Industries PlcSyringe
US5152965 *Jun 2, 1989Oct 6, 1992Abbott LaboratoriesFor controlled storage and mixing; selectively displaceable seal allows reagent to flow through hollow plunger to mix with buffer or diluent; clinical chemical analyses
US5260957Oct 29, 1992Nov 9, 1993The Charles Stark Draper Laboratory, Inc.Quantum dot Laser
US5293050 *Mar 25, 1993Mar 8, 1994International Business Machines CorporationSemiconductor quantum dot light emitting/detecting devices
US5354707Nov 9, 1993Oct 11, 1994International Business Machines CorporationForming intrinsic silicon epitaxial layer on doped silicon layer of first conductivity type, forming quantum dots, embedding in second intrinsic epitaxial layer, forming doped layer of second conductivity type
US5419445Jun 24, 1994May 30, 1995Kaesemeyer; David M.Container for storing, mixing and dispensing
US5422489Jan 24, 1994Jun 6, 1995Bhargava; Rameshwar N.Light emitting device
US5433328May 17, 1994Jul 18, 1995Baron; Moises S.Baby bottle extension assembly having storage chamber and release mechanism
US5505928Apr 21, 1994Apr 9, 1996The Regents Of University Of CaliforniaReacting a group iii metal source with a group v anion source in a liquid phase at elevated temperature in the presence of a crystallite growth terminator such as pyridine or quinoline
US5525377Jun 7, 1995Jun 11, 1996U.S. Philips CorporationMethod of manufacturing encapsulated doped particles
US5537000Apr 29, 1994Jul 16, 1996The Regents, University Of CaliforniaElectroluminescent devices formed using semiconductor nanocrystals as an electron transport media and method of making such electroluminescent devices
US5585640Jan 11, 1995Dec 17, 1996Huston; Alan L.Luminescent glass comprising glass matrix doped with nanocrystalline semiconductor particles, activator; transparent to luminescent emissions
US5613140Oct 11, 1994Mar 18, 1997Sony CorporationQuantum dot-tunnel device which can be selectively excited by a first light emitting source and the information thus stored can be read with a second light emitting source
US5677545Sep 12, 1994Oct 14, 1997MotorolaOrganic light emitting diodes with molecular alignment and method of fabrication
US5751018Apr 29, 1994May 12, 1998The Regents Of The University Of CaliforniaSemiconductor nanocrystals covalently bound to solid inorganic surfaces using self-assembled monolayers
US5794802Mar 4, 1997Aug 18, 1998Caola; JosephContainer for separation, storage, and mixing of ingredients
US5984141 *May 20, 1998Nov 16, 1999Gibler; Gregory A.Beverage storage and mixing device
US6054495Sep 29, 1998Apr 25, 2000The United States Of America As Represented By The Secretary Of The NavySynthesis of unagglomerated metal nano-particles at membrane interfaces
US6103868Dec 27, 1996Aug 15, 2000The Regents Of The University Of CaliforniaOrganically-functionalized monodisperse nanocrystals of metals
US6139585Mar 11, 1998Oct 31, 2000Depuy Orthopaedics, Inc.An implantable prostheses are coated a carbonated nano-crystalline bone apatite chemically bonded to substrate; a rapid and effective bone ingrowth
US6152296Nov 6, 1998Nov 28, 2000Shih; Kuang-ShengAdditive holder for a pet bottle
US6157047Aug 28, 1998Dec 5, 2000Kabushiki Kaisha ToshibaLight emitting semiconductor device using nanocrystals
US6207229Aug 5, 1999Mar 27, 2001Massachusetts Institute Of TechnologyPreparing coated nanocrystal capable of light emission, comprising introducing substantially monodisperse core population, wherein each member comprises a first semiconductor material, into coordinating solvent, overcoating
US6221416Jun 16, 1999Apr 24, 2001Innova Pure Water Inc.Dynamically flowing bottled drinking water through porous, water soluble, solid element comprising a flavoring, dietary mineral, vitamin, and/or medicines positioned within a filter in the bottle neck
US6294401Jun 17, 1999Sep 25, 2001Massachusetts Institute Of TechnologyNanoparticle-based electrical, chemical, and mechanical structures and methods of making same
US6322901Nov 13, 1997Nov 27, 2001Massachusetts Institute Of TechnologyHighly luminescent color-selective nano-crystalline materials
US6372270May 16, 2000Apr 16, 2002Sean P. DennyDrink mix apparatus for making personal quantities of beverage
US6379635Aug 9, 1996Apr 30, 2002Imperial College Of Science, Technology & MedicineOf first and second different ions, by contacting a complex containing the two ions with a dispersing medium at temperature to allow formation by pyrolysis of the nanocrystalline material; forming cadmium selenide; optics
US6445009 *Aug 8, 2000Sep 3, 2002Centre National De La Recherche ScientifiqueLight emitting diodes
US6447698Sep 17, 1999Sep 10, 2002Sony CorporationMethod for producing light-emitting substance
US6501091Oct 7, 1998Dec 31, 2002Massachusetts Institute Of TechnologyQuantum dot white and colored light emitting diodes
US6506564Jun 26, 2000Jan 14, 2003Nanosphere, Inc.Nanoparticles having oligonucleotides attached thereto and uses therefor
US6527110May 31, 2001Mar 4, 2003Brett MoscovitzDevice for storing and dispensing a substance by mating with a container and associated methods
US6569329May 8, 2000May 27, 2003Innova Pure Water Inc.Personal water filter bottle system
US6576291Dec 8, 2000Jun 10, 2003Massachusetts Institute Of TechnologyPreparation of nanocrystallites
US6607829Jul 26, 2000Aug 19, 2003Massachusetts Institute Of TechnologyTellurium-containing nanocrystalline materials
US6644471May 24, 2002Nov 11, 2003Michael R. AndersonDispensing capsule for a liquid container
US6797412Apr 11, 2000Sep 28, 2004University Of ConnecticutUse of cladding layer material that has a higher band gap than the core with similar lattice constant results in a pseudomorphic cladded quantum dot
US6816525 *Oct 5, 2001Nov 9, 2004Andreas StintzQuantum dot lasers
US6846565Mar 28, 2002Jan 25, 2005Board Of Regents, The University Of Texas SystemHeating a mixture of a metal compound, especially a Group IV metal organometallic precursor, and a capping agent (especially one that provides oxidation resistance) at a temperature wherein the precursor decomposes
US6864626Jun 2, 1999Mar 8, 2005The Regents Of The University Of CaliforniaMulticolor pixel; variations in particle sizes
US6886686Apr 9, 2004May 3, 2005Michael R. AndersonDispensing capsule for a liquid container
US7055685Apr 27, 2005Jun 6, 2006Brent PattersonMixing cap and method for use thereof
US20010005495Aug 9, 1996Jun 28, 2001Paul O'brienProcess for preparing a nanocrystalline material
US20020090426Mar 18, 2002Jul 11, 2002Denny Sean P.Methods and apparatus for making personal quantities of beverage
US20030003300 *Mar 28, 2002Jan 2, 2003Korgel Brian A.Light-emitting nanoparticles and method of making same
US20030017264Jul 17, 2002Jan 23, 2003Treadway Joseph A.Luminescent nanoparticles and methods for their preparation
US20030042850Sep 3, 2002Mar 6, 2003Dietrich BertramElectroluminescent device comprising quantum dots
US20030072850Oct 16, 2002Apr 17, 2003Burniski Edward WilliamBottle cap drink mix reservoir
US20040200740Oct 14, 2003Oct 14, 2004Cho Young KookCap device for mixing different kinds of materials separately contained therein and in bottle
US20040200742Oct 17, 2003Oct 14, 2004Cho Young KookCap device for mixing different kinds of materials separately contained therein and in bottle
US20040265622Jun 24, 2003Dec 30, 2004Eastman Kodak CompanyLight emitting display
JP2003081357A Title not available
JP2004083022A Title not available
WO1996010282A1Sep 29, 1995Apr 4, 1996British TelecommOptical fibre with quantum dots
WO1997010175A1Aug 9, 1996Mar 20, 1997Brien Paul OProcess for preparing a nanocrystalline material
WO1999026299A1Nov 10, 1998May 27, 1999Massachusetts Inst TechnologyHighly luminescent color-selective materials
WO2005004253A1Jun 22, 2004Jan 13, 2005Thomas Nelson BlantonAn organic light emitting display where the same luminescent dye is modified in such a manner as to luminesce at various desired wavelengths
WO2005017951A2Aug 1, 2003Feb 24, 2005Ultradots IncQuantum dots, nanocomposite materials with quantum dots, optical devices with quantum dots, and related fabrication methods
Non-Patent Citations
Reference
1Alivisatos, "Perspectives on the Physical Chemistry of Semiconductor Nanocrystals," J. Phys. Chem. 1996(100):13226-13239, 1996.
2 *Coe, et al., "Electroluminescence From Single Monolayers of Nanocrystals in Molecular Organic Devices," Nature, 420(19) Dec. 26, 2002.
3Colvin, et al., "Light-emitting diodes made from cadmium selenide nanocrystals and a semiconducting polymer," Nature 370(6488):354-357, Aug. 4, 1994.
4Dabbousi, et al., "(CdSe)ZnS core-shell quantum dots: synthesis and characterization of a size series of highly luminescent nanocrystallites," J. Phys. Chem. B 101(46):9463-9475, Nov. 13, 1997.
5Dabbousi, et al., "Electroluminescence from CdSe quantum-dot/polymer composites," Appl. Phys. Lett. 66(11):1316-1318, Mar. 13, 1995.
6Danek, et al., "Synthesis of Luminescent Thin-Film CdSe/ZnSe Quantum Dot Composites Using CdSe Quantum Dots Passivated with an Overlayer of ZnSe," Chem. Mater. 8(1):173-180, 1996.
7Diehl, "Fraunhofer LUCOLEDs to replace lamps," III-Vs Rev. 10(1), 1997.
8 *Ekimov, "Absorption and Intensity-dependent photoluminescence measurements on CdSe quantum dots: assignment of the first elecrtronic transitions," Journal of the Optical Society of America, vol. 10, No. 1, 100-107 (1992).
9 *Ekimov, "Dynamics of Nonlinear Optical Response of CuBr-Doped Glasses," Superlattices and Microstructures, vol. 13, No. 2, 199-202 (1993).
10 *Ekimov, "Nonlinear Optical Properties of Semiconductor Microcrystals," JETP Lett., vol. 46, No. 10, 495-499 (1987).
11 *Ekimov, "Oscillations of Polarization of Recombination Radiation of a Variable Gap Semiconductor in a Magnetic Field," JETP Lett., vol. 25, No. 12, 526-528 (1977).
12 *Ekimov, "Preparation and Investigation of SiO2 Films Activated by CDS Semiconductor Nanocrystals," Soviet Physics Semiconductors, vol. 26, No. 1, 57-59.
13Ekimov, A. I., "Surface Recombination of Nonequilibrium Electron-Hole Plasma in Laser-Modified Semiconductor-Doped Glasses," Solid State Communications, vol. 87, No. 6, 577-580 (1993).
14Ekimov, A.I. et al., "Anger ionization of semiconductor quantum drops in a glass matrix," Journal of Luminescence 47 (1990) 113-127 North-Holland.
15Ekimov, A.I. et al., "CdS nanocrystal growth in thin silica films: evolution of size distribution function,"Journal of Crystal Growth 184/185 (1998) 360-364.
16Ekimov, A.I. et al., "Dimensional Effects in Luminescence Spectra of Zero-Dimensional Semiconductor Structures," Bulletin of the Russian Academy of Sciences, vol. 56, No. 2, pp. 154-157, Feb. 1992.
17Ekimov, A.I. et al., "Donor-like Exciton in Zero-Dimension Semiconductor Structures," Solid State Communications, vol. 69, No. 5, pp. 565-568, 1989.
18Ekimov, A.I. et al., "Dynamics of excitons in CuBr nanocrystals: Spectral-hole burning and transient four-wave-mixing measurements," Physical Review B, vol. 57, No. 3, Jan. 15, 1998-I, 1774-1783.
19Ekimov, A.I. et al., "Effects of Resonance on Low-Frequency Raman Scattering From Semiconductor Nanocrystals," Radiation Effects and Defects in Solids, 1995, vol. 137, pp. 45-50.
20Ekimov, A.I. et al., "Enhancement of electron-hole exchange interaction in CdSe nanocrystals; A quantum confinement effect," Physical Review B, vol. 53, No. 3, Jan. 15, 1996-I, 1336-1342.
21Ekimov, A.I. et al., "Enhancement of Exciton Exchange Interaction by Quantum Confinement in CdSe Nanocrystals," Jpn. J. Appl. Phys, vol. 34, 12-14 (1994).
22Ekimov, A.I. et al., "Fast switching of the transmission of light by glasses activated with CdS microcrystals," Sov. Phys. Semicond., vol. 25, No. 2, 164-166 (1991).
23Ekimov, A.I. et al., "Generation of reflected second harmonic at semiconductor quantum dots," JETP Letters, vol. 55, No. 8, 435-439 (1992).
24Ekimov, A.I. et al., "Growth and optical properties of semiconductor nanocrystals in a glass matrix," Journal of Luminescence 70 (1996) 1-20.
25Ekimov, A.I. et al., "Growth of CdS nanocrystals in silicate glasses and in thin SiO<SUB>2 </SUB>films in the Initial states of the phase separation of a solid solution," Semiconductors, 28 (5), May 1994, 486-493.
26Ekimov, A.I. et al., "Growth of CdSe nanocrystals in ion-implanted SiO<SUB>2 </SUB>films," Journal of Crystal Growth 151 (1995) 38-45.
27Ekimov, A.I. et al., "Influence of high hydrostatic pressures on the exciton spectrum of CdS microcrystals in glass," Sov. Phys. Semicond. 23(9), Sep. 1989, pp. 965-966.
28Ekimov, A.I. et al., "Interface effects on the properties of confined excitons in CuCl microcrystals," Journal of Luminescence 60 & 61 (1994) 396-399.
29Ekimov, A.I. et al., "Nonlinear Optics of Semiconductor-Doped Glasses," Phys. Stat. Sol. (b) 150, (1988) pp. 627-633.
30Ekimov, A.I. et al., "Optical Properties of Oxide Glasses Doped by Semiconductor Nanocrystals," Radiation Effects and Defects in Solids, 1995, vol. 134, pp. 11-22.
31Ekimov, A.I. et al., "Optical Properties of Semiconductor Quantum Dots in Glass Matrix," Physica Scripta. vol. T39, 217-222 (1991).
32Ekimov, A.I. et al., "Optics of Zero Dimensional Semiconductor Systems, Acta Physica Polonica A," vol. 79 (1991), No. 1, pp. 5-14.
33Ekimov, A.I. et al., "Photoionization of semiconducting microcrystals in glass," Sov. Phys. Solid State 31(1), Jan. 1989, pp. 149-151.
34Ekimov, A.I. et al., "Photoluminescence of quasizero-dimensional semiconductor structures," Sov. Phys. Solid State 31(8), Aug. 1989, pp. 1385-1393.
35Ekimov, A.I. et al., "Polaron and Exciton-Phonon Complexes in CuCl Nanocrystals," Physical Review Letters, vol. 74, No. 9, Feb. 27, 1995, p. 1645.
36Ekimov, A.I. et al., "Quantization of the energy spectrum of holes in the adiabatic potential of the electron," JETP Lett., vol. 43, No. 6, Mar. 25, 1986, pp. 376-379.
37Ekimov, A.I. et al., "Quantum Size Effect in Semiconductor Microcrystals," Solid State Communications, vol. 56, No. 11, pp. 921-924, 1985.
38Ekimov, A.I. et al., "Quantum size effect in the optical spectra of semiconductor microcrystals," Sov. Phys. Semicond. 16(7), Jul. 1982, pp. 775-778.
39Ekimov, A.I. et al., "Quantum size effect in three-dimensional microscopic semiconductor crystals," JETP Lett., vol. 34, No. 6, Sep. 20, 1981, pp. 345-349.
40Ekimov, A.I. et al., "Quantum-Size Stark Effect in Semiconductor Microcrystals," Journal of Luminescence 46 (1990) 97-100 North-Holland.
41Ekimov, A.I. et al., "Rapid Processes of Darkening and Bleaching in CdS Doped Glasses," Superlattices and Microstructures vol. 10, No. 3, 307-310 (1990).
42Ekimov, A.I. et al., "Resonance Raman Spectroscopy of Electron-Hole Pairs-Polar Phonon Coupling in Semiconductor Quantum Microcrystals," Solid State Communications, vol. 78, No. 10, pp. 853-856, 1991.
43Ekimov, A.I. et al., "Size dependence of acoustic and optical vibrational modes of CdSe nanocrystals in glasses," Journal of Non-Crystalline Solids 197 (1996) 238-246.
44Ekimov, A.I. et al., "Size quantization of the electron energy spectrum in a microscopic semiconductor crystal," JETP Lett., vol. 40, No. 8, Oct. 25, 1984, pp. 1136-1139.
45Ekimov, A.I. et al., "Size-dependent Electron-Hole Exchange Interaction in CdSe Quantum Dots, Il Nuovo Cimento," vol. 17, Nos. 11-12, (1995) 1407-1412.
46Ekimov, A.I. et al., "Size-selective resonant Raman scattering in CdS doped glasses," Physical Review B, vol. 57, No. 1, Jan. 1, 1998-I, 341-346.
47Ekimov, A.I. et al., "Spectra and Decay Kinetics of Radiative Recombination in CdS Microcrystals," Journal of Luminescence 46 (1990) 83-95 North-Holland.
48Ekimov, A.I. et al., "Spin-flip and acoustic-phonon Raman scattering in CdS nanocrystals," Physical Review B, vol. 58, No. 4, 15 (Jul. 1998-II), 2077-2087.
49Ekimov, A.I. et al., "Subpicosecond dynamics of confined excitons and optical nonlinearities of CuCl quantum dots," Journal of Luminescence 66 & 67 (1996) 406-409.
50Ekimov, A.I. et al., "Subpicosecond dynamics of confined excitons in CuCl nanocrystals," Materials Science and Engineering A217/218 (1996) 167-170.
51Ekimov, A.I. et al., "Time-Resolved Luminescence of CdSe Microcrystals," Solid State Communications, vol. 74, No. 7, pp. 555-557, 1990.
52Ekimov, A.I., et al., "Quantum Confined Atoms of Doped ZnO Nanocrystals," Phys. Stat. Sol (b) 229, No. 2, 897-901 (2002).
53Empedocles, et al., "Photoluminescence Spectroscopy of Single CdSe Nanocrystallite Quantum Dots," Phys. Rev. Lett. 77(18):3873-3876, Oct. 1996.
54Empedocles, et al., "Quantum-Confined Stark Effect in Single CdSe Nanocrystallite Quantum Dots," Science 278:2114-2117, Dec. 1997.
55Guha, et al., "Hybrid organic-inorganic semiconductor-based light-emitting diodes," J. Appl. Phys. 82(8):4126-4128, Oct. 15, 1997.
56Hines, et al., "Synthesis and Characterization of Strongly Luminescing ZnS-Capped CdSe Nanocrystals," J. Phys. Chem. 100:468-471, Jan. 1996.
57Kagan, et al., "Electronic Energy Transfer in CdSe Quantum Dot Solids," Phys. Rev. Lett. 76(9):1517-1520, 1996.
58Kagan, et al., "Long-range resonance trasfer of electronic excitations in close-packed CdSe quantum-dot solids," Phys. Rev. B 54(12):8633-8643, 1996.
59Kortan, et al., "Nucleation and Growth of CdSe on ZnS Quantum Crystallite Seeds, and Vice Versa, in Inverse Micelle Media," J. Am. Chem. Soc. 112:1327-1332, 1990.
60Kuno, et al., "The band edge luminescence of surface modified CdSe nanocrystallites: Probing the luminescing state," J. Chem. Phys. 106(23):9869-9882, Jun. 1997.
61Lawless, et al., "Bifunctional Capping of CdS Nanoparticles and Bridging to TiO2," J. Phys. Chem. 99:10329-10335, 1995.
62 *Leatherdale, et al., "Photoconductivity in CdSe Quantum Dot Solids," Phys. Rev. B, vol. 62, No. 4, 2669-2680 (Jul. 15, 2000).
63Matsumoto, et al., "Preparation of Monodisperse CdS Nanocrystals by Size Selective Photocorrosion," J. Phys. Chem 100(32):13781-13785, 1996.
64Mattoussi et al., "Electroluminescence from heterostructures of poly(phenylene vinylene) and inorganic CdSe nanocrystals," J. Appl. Phys. 83(12):7965-7974, 1998.
65Murray et al., Annu. Rev. Mat. Sci., 30, 545-610 (2000).
66Murray, et al., "Synthesis and Characterization of Nearly Monodisperse CdE(E=S, Se, Te) Semiconductor Nanocrystallites," J. Am. Chem. Soc. 115(19):8706-8715, 1993.
67Nirmal, et al., "Fluorescence Intermittency in single Cadmium Selenide Nanocrystals," Nature 383:802-804, Oct. 1996.
68Schlamp et al., "Improved efficiencies in light emitting diodes made with CdSe (CdS) core/shell type nanocrystals and a semiconducting polymer", J. Appl. Phys 82(11):5837-5842, 1997.
69Spanhel et al., "Photochemistry of Colloidal Semiconductors. Surface Modification and Stability of Strong Luminescing CdS Particles", J. Am. Chem. Soc., 109 (19), pp. 5649-5655, (1987).
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Classifications
U.S. Classification428/206, 428/328, 428/323, 428/330, 428/208
International ClassificationB32B3/00, B32B5/16
Cooperative ClassificationB82Y30/00, B82Y20/00, B05D1/34, H01L51/5048, B05D1/005, B22F1/0018, H01L51/5012, B05D7/52, B22F1/02
European ClassificationB82Y30/00, B82Y20/00, B22F1/02, B22F1/00A2B4
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